In a known refrigerant circuit used in a method for cooling a hydrocarbon stream, e.g. in order to produce an LNG stream, the refrigerant is successively compressed in a compressor arrangement, cooled against e.g. water or air in a first heat exchanger, expanded and evaporated in a second heat exchanger (usually a cryogenic heat exchanger) where the refrigerant cools at least the natural gas stream to be cooled. The spent refrigerant leaving the second heat exchanger is again compressed, cooled and so on.
An example of a known method for cooling a hydrocarbon stream is disclosed in U.S. Pat. No. 5,826,444. U.S. Pat. No. 5,826,444 relates to a process and to a device allowing to liquefy a fluid or a gaseous mixture consisting at least partly of a mixture of hydrocarbons, for example natural gas.
The compressor arrangement used for compressing the refrigerant in the known refrigerant circuits usually comprises only one or more centrifugal compressors and no axial compressors, due to the fixed optimal pressure ratio of an axial compressor.
The above is even more true in the liquefaction of a natural gas stream using a mixed refrigerant evaporating in multiple cryogenic heat exchangers at multiple pressure levels in the refrigerant cycle, thereby resulting in various refrigerant streams at different pressure levels to be cycled back to the compressor arrangement for recompressing. Normally, axial compressors are not suitable to handle the typical pressure levels in a mixed refrigerant circuit with multiple cryogenic heat exchangers, due to the fixed optimal pressure ratios of the axial compressors.